We have prepared antibody against purified nitrate reductase isolated from membranes of E. coli, and by immune precipitation we are examining both membranes and cytoplasm from various chlorate-resistant mutants for the various subunits of the enzyme. We are also attempting to determine how this enzyme is attached to the membrane. We are examining the specificity of the lactoperoxidase-iodine labeling technique by determining if the single tyrosine of the murein lipoprotein can be labeled, since the location of this tyrosine on the inner surface of the outer membrane is known quite precisely. We have discovered that the outer membrane of E.coli contains several major polypeptides of the same molecular weight, and that the amounts of these various polypeptides change as a function of rate of growth or catabolite repression. These different polypeptides are being identified by cyanogen bromide peptide mapping, since some of them cannot be separated by SDS gel electrophoresis. We are examining enterotoxin-producing strains of E. coli to determine if the enterotoxin affects the cyclic AMP level of the bacterial cells.